Soil drought and circulation types in a longitudinal transect over central Europe

Abstract

Among the variables that can be employed to characterize agricultural drought, soil drought is of particular importance. This contribution uses gridded soil‐drought values calculated from the SoilClim model for the 1961–2019 period to analyse soil drought episodes (based on the 10th percentile) in four lowlands, relatively homogeneous regions in central Europe that provide a longitudinal transect over central Europe. These areas are predominantly located at altitudes of below 400 m asl and include central Bohemia, southern Moravia and an adjacent part of Slovakia, southern Slovakia and eastern Slovakia. The results indicate that, after 1990, such episodes occurred largely in the summer half‐year (April–September), accompanied by an increasing linear trend in the 1961–2019 period, while the situation was reversed in the winter half‐year (October–March). Selected drought episodes are further divided into three phases (Phase I – origin, Phase II – course, Phase III – end) and investigated separately in terms of precipitation and objective classification of circulation types based on flow strength, direction and vorticity. Decreases in the frequency of precipitation‐rich cyclonic and the directional types associated with higher daily precipitation totals, together with increases in precipitation‐poor anticyclonic types, were responsible for soil‐drought Phases I and II, with the opposite pertaining to Phase III. Differences in the effects of circulation types on precipitation and soil‐drought occurrence were considerable, particularly for central Bohemia compared with the other three regions. The results obtained are also discussed with respect to data uncertainty and their broader spatiotemporal context.

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